U.S. patent application number 13/020478 was filed with the patent office on 2011-08-11 for gel point modification in alkyd resin manufacture.
Invention is credited to William M. Allen, JR., Isao Noda.
Application Number | 20110196108 13/020478 |
Document ID | / |
Family ID | 43923721 |
Filed Date | 2011-08-11 |
United States Patent
Application |
20110196108 |
Kind Code |
A1 |
Noda; Isao ; et al. |
August 11, 2011 |
Gel Point Modification In Alkyd Resin Manufacture
Abstract
Disclosed herein is a metastable, liquid alkyd resin precursor
that has exceeded its gel point, but is not a gel. The precursor
includes a gel point modifier and a prepolymer liquid. The
prepolymer liquid includes oligomeric polyesters, polyols, and an
excipient selected from the group consisting of polyfunctional
acids, anhydrides, and mixtures thereof. Also disclosed herein are
methods of making the metastable, liquid alkyd resin precursor, and
methods of using the metastable, liquid alkyd resin precursor to
form fully cross-linked alkyd resins.
Inventors: |
Noda; Isao; (Fairfield,
OH) ; Allen, JR.; William M.; (Liberty Twsp.,
OH) |
Family ID: |
43923721 |
Appl. No.: |
13/020478 |
Filed: |
February 3, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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61302076 |
Feb 5, 2010 |
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Current U.S.
Class: |
525/418 |
Current CPC
Class: |
C08G 63/914
20130101 |
Class at
Publication: |
525/418 |
International
Class: |
C08G 63/91 20060101
C08G063/91 |
Claims
1. A liquid alkyd resin precursor comprising: (a) a gel point
modifier; and (b) prepolymer liquid comprising oligomeric
polyesters, polyols, and an excipient selected from the group
consisting of polyfunctional acids, anhydrides, and mixtures
thereof; the prepolymer liquid having reached about 50% to about
90% of its corrected, theoretical gel point, p.sub.gel(corrected),
as determined by Formula II: p gel ( corrected ) = 2 ( k ) f
average Formula II ##EQU00005## wherein k is about 0.9 to about 1,
and f.sub.average is the sum of (i) the number of alcohol moieties
on the polyol, (ii) the number of acid moieties on the
polyfunctional acid, and (iii) twice the number of anhydride
moieties on the anhydride, divided by the total number of polyols,
polyfunctional acids, and anhydrides.
2. The liquid alkyd resin precursor of claim 1, wherein the
prepolymer liquid is at about 80% to about 85% of its theoretical
gel point.
3. The liquid alkyd resin precursor of claim 1, wherein k is about
0.95.
4. The liquid alkyd resin precursor of claim 1 having a viscosity
of about 0.1 kg m.sup.-1s.sup.-1to about 10,000 kg m.sup.-1s.sup.-1
at about 160.degree. C. to about 220.degree. C.
5. The liquid alkyd resin precursor of claim 1, wherein the polyol
is selected from the group consisting of glycerol, 1,3-propanediol,
pentaerythritol, dipentaerythritol, trimethylolpropane,
trimethylolethane, ethylene glycol, diethylene glycol,
polyglycerol, diglycerol, triglycerol, 1,2-propanediol,
1,4-butanediol, neopentylglycol, hexanediol, hexanetriol,
erythritol, xylitol, maltitol, mannitol, polyvinyl alcohol, and
mixtures thereof.
6. The liquid alkyd resin precursor of claim 5, wherein the polyol
is selected from the group consisting of glycerol, pentaerythritol,
trimethylolpropane, trimethylolethane, and mixtures thereof.
7. The liquid alkyd resin precursor of claim 1, wherein the
excipient is selected from the group consisting of adipic acid,
maleic acid, succinic acid, sebacic acid, suberic acid, fumaric
acid, glutaric acid, phthalic acid, malonic acid, isophthalic acid,
terephthalic acid, azelaic acid, dimethylolpropionic acid, maleic
anhydride, succinic anhydride, phthalic anhydride, trimellitic
anhydride, polyacrylic acid, polymethacrylic acid, and mixtures
thereof.
8. The liquid alkyd resin precursor of claim 6, wherein the
excipient is an anhydride selected from the group consisting of
maleic anhydride, succinic anhydride, phthalic anhydride, and
mixtures thereof.
9. The liquid alkyd resin precursor of claim 1, wherein the molar
ratio of total acid moieties on the polyfunctional acid to total
alcohol moieties on the polyol is about 10:1 to about 1:10.
10. The liquid alkyd resin precursor of claim 9, wherein the molar
ratio is about 3:1 to about 1:3.
11. The liquid alkyd resin precursor of claim 10, wherein the molar
ratio is about 1:1.
12. The liquid alkyd resin precursor of claim 1, wherein the molar
ratio of total anhydride moieties on the anhydride to total alcohol
moieties on the polyol is about 5:1 to about 1:5.
13. The liquid alkyd resin precursor of claim 12, wherein the molar
ratio is about 1.5:1 to about 1:1.5.
14. The liquid alkyd resin precursor of claim 13, wherein the molar
ratio is about 0.5:1.
15. The liquid alkyd resin precursor of claim 1, wherein the gel
point modifier comprises at least three functional groups selected
from the group consisting of acids, alcohols, amines, thiols,
epoxides, anhydrides, and mixtures thereof.
16. The liquid alkyd resin precursor of claim 15, wherein the gel
point modifier is selected from the group consisting of glycerol,
pentaerythritol, dipentaerythritol, trimethylolpropane,
trimethylolethane, polyglycerol, diglycerol, triglycerol,
hexanetriol, erythritol, xylitol, maltitol, mannitol, polyvinyl
alcohol, succinic acid, trimellitic anhydride, polyacrylic acid,
polymethacrylic acid, and mixtures thereof.
17. The liquid alkyd resin precursor of claim 16, wherein the gel
point modifier is selected from the group consisting of
pentaerythritol, trimethylolpropane, trimethylolethane, polyacrylic
acid, and mixtures thereof.
18. The liquid alkyd resin precursor of claim 15, wherein the gel
point modifier is selected from the group consisting of derivatized
tall oil, corn oil, soybean oil, sunflower oil, safflower oil,
linseed oil, perilla oil, cotton seed oil, tung oil, peanut oil,
oiticica oil, hempseed oil, marine oil, dehydrated castor oil, and
mixtures thereof.
19. The liquid alkyd resin precursor of claim 1, wherein the gel
point modifier is present in an amount of about 0.1 wt. % to about
10 wt. %, based on the total weight of the precursor.
20. The liquid alkyd resin precursor of claim 17, wherein the gel
point modifier is present in an amount of about 0.5 wt. % to about
5 wt. %, based on the total weight of the precursor.
21. The liquid alkyd resin precursor of claim 20, wherein the gel
point modifier is present in an amount of about 1 wt. %, based on
the total weight of the precursor.
22. A method of preparing a liquid alkyd resin precursor, the
method comprising adding a gel point modifier to a prepolymer
liquid to form the liquid, alkyd resin precursor, wherein the
prepolymer liquid comprises oligomeric polyesters, polyols, and an
excipient selected from the group consisting of polyfunctional
acids, anhydrides, and mixtures thereof; the prepolymer liquid
having reached about 50% to about 90% of its corrected, theoretical
gel point p.sub.gel(corrected).
23. The method of claim 22, wherein the gel point modifier
comprises at least three functional groups selected from the group
consisting of acids, alcohols, amines, thiols, epoxides,
anhydrides, and mixtures thereof.
24. The method of claim 23, wherein the gel point modifier is
selected from the group consisting of glycerol, pentaerythritol,
dipentaerythritol, trimethylolpropane, trimethylolethane,
polyglycerol, diglycerol, triglycerol, hexanetriol, erythritol,
xylitol, maltitol, mannitol, polyvinyl alcohol, succinic acid,
trimellitic anhydride, polyacrylic acid, polymethacrylic acid, and
mixtures thereof.
25. The method of claim 24, wherein the gel point modifier is
selected from the group consisting of pentaerythritol,
trimethylolpropane, trimethylolethane, polyacrylic acid, and
mixtures thereof.
26. The liquid alkyd resin precursor of claim 23, wherein the gel
point modifier is selected from the group consisting of derivatized
tall oil, corn oil, soybean oil, sunflower oil, safflower oil,
linseed oil, perilla oil, cotton seed oil, tung oil, peanut oil,
oiticica oil, hempseed oil, marine oil, dehydrated castor oil, and
mixtures thereof.
27. The method of claim 22, wherein the gel point modifier is added
in an amount of about 0.1 wt % to about 10 wt %, based on the total
weight of the precursor.
28. The method of claim 27, wherein the gel point modifier is added
in an amount of about 0.5 wt. % to about 5 wt. %, based on the
total weight of the precursor.
29. The method of claim 28, wherein the gel point modifier is added
in an amount of about 1 wt %, based on the total weight of the
precursor.
30. A method of preparing fully cross-linked alkyd resin, the
method comprising: (a) adding a gel point modifier to a prepolymer
liquid to form a liquid, alkyd resin precursor; and, (b) heating
the alkyd resin precursor to a temperature sufficient to promote
further condensation, while concurrently removing water formed
during condensation to form fully cross-linked alkyd resin, wherein
the prepolymer liquid in step (a) comprises oligomeric polyesters,
polyols, and an excipient selected from the group consisting of
polyfunctional acids, anhydrides, and mixtures thereof; the
prepolymer liquid having reached about 50% to about 90% of its
corrected, theoretical gel point p.sub.gel(corrected).
31. The method of claim 22 or 30, wherein the corrected,
theoretical gel point, p.sub.gel(corrected), is determined by
Formula II: p gel ( corrected ) = 2 ( k ) f average Formula II
##EQU00006## wherein k is about 0.9 to about 1, and f.sub.average
is the sum of (i) the number of alcohol moieties on the polyol,
(ii) the number of acid moieties on the polyfunctional acid, and
(iii) twice the number of anhydride moieties on the anhydride,
divided by the total number of polyols, polyfunctional acids, and
anhydrides.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of U.S. Provisional
Application No. 61/302,076 filed Feb. 5, 2010.
FIELD OF THE INVENTION
[0002] This disclosure relates to a metastable, liquid alkyd
material that has exceeded its gel point but is not a gel, methods
of making the liquid alkyd material, and uses thereof.
BACKGROUND OF THE INVENTION
[0003] Alkyd resins are polymer networks comprised of ester
cross-links that are formed by the condensation of polyols with
polyfunctional acids, anhydrides, or a mixture of polyfunctional
acids and anhydrides. Upon curing, alkyd resins exhibit properties
characteristic of thermoset resins.
[0004] Thermoset resins are high molecular weight polymers that
irreversibly convert into infusible (i.e. incapable of being
melted) and insoluble (i.e. cannot be dissolved in a solvent)
polymer networks by curing. Curing refers to the toughening or
hardening of a polymer material by the cross-linking of polymer
chains. "Cross-linking" is the process of bonding one polymer chain
to another. Prior to curing, thermoset materials are typically
liquid or malleable, and exist as a reactive mixture of monomers
and oligomers. This reactive mixture is introduced into a mold
where it is cross-linked to create a rigid, three-dimensional
network of oligomer chains with a desired shape or form.
[0005] The formation of alkyd resins occurs in three stages that
are schematically depicted in the sole drawing. During Stage I, a
polyol and an excipient selected from the group consisting of a
polyfunctional acid, an anhydride, or mixtures thereof, is heated
to promote rapid esterification of the polyol and excipient
monomers. As a result of this condensation reaction, a water
by-product is violently liberated from the reaction mixture. Stage
I ends when at least about 50% of the polyol and the excipient
monomers have undergone condensation (a) to result in the formation
of a prepolymer liquid comprising oligomeric polyesters, polyols,
and the excipient. This prepolymer liquid is free-flowing at an
elevated temperature with a low viscosity, demonstrating that it is
not extensively cross-linked During Stage II (b), condensation of
the monomers and oligomers in the prepolymer liquid continues, but
at a significantly slower rate than during Stage I. The molecular
weight and viscosity of the prepolymer liquid increases during this
stage of alkyd resin formation, although the liberation rate of the
water by-product decreases significantly and is easily controlled.
After at least about 70% to about 80% of the polyol and excipient
have undergone condensation, depending on the specific polyol and
excipient used, the prepolymer material congeals into a solid mass.
This congealment is termed the "gel point" of the condensation (c).
At the gel point, a three-dimensional network that is swollen with
prepolymers is formed, with most of the prepolymer molecules not
yet cross-linked Beyond the gel point, the alkyd material is
insoluble and infusible, even at an elevated temperature, and the
shape of the material is set. During Stage III of alkyd resin
formation, additional condensation of the oligomers and monomers
occurs until the gel is fully cross-linked and exhibits properties
that are characteristic of thermoset resins (d). This resin is
infusible and does not swell in the presence of solvents.
[0006] The gel point of alkyd resins is a useful indicator of the
onset of the formation of a cross-linked thermoset resin with good
structural integrity and dimensional stability. Several useful
models have been proposed to predict the gel point of a
condensation reaction involving polyfunctional monomers. The
simplest and oldest model is "Gel Theory" proposed by Carrothers
(W. H. Carrothers, Trans. Faraday Soc. 32, 39 (1936)). According to
Carrothers' theory, the degree of conversion of monomer to oligomer
at the gel point (p.sub.gei) can be estimated by Formula I:
p gel = 2 f average Formula I ##EQU00001##
wherein f.sub.average (i.e. the average functionality of a reaction
mixture) is the sum of (i) the number of alcohol moieties on the
polyol, (ii) the number of acid moieties on the polyfunctional
acid, and (iii) twice the number of anhydride moieties on the
anhydride, divided by the total number of polyols, polyfunctional
acids, and anhydrides.
[0007] Although the Carrothers' model is a good predictor of the
degree of conversion of monomer to oligomer at the gel point, it
often overestimates the gel point by about 5% to about 10% because
it neglects important factors such as the effect of temperature and
other thermodynamic parameters. Adding a heuristic correction
factor (k) as shown in Formula II, wherein k is about 0.9 to about
1, allows a closer estimation of the actual onset of gelation:
p gel ( corrected ) = 2 ( k ) f average Formula II ##EQU00002##
wherein f.sub.average is as defined above. Therefore, according to
Carrothers' theory, the higher the number of functional groups on
an individual monomers, the lower the degree of monomer conversion
at the corrected, theoretical gel point, p.sub.gel(corrected).
[0008] Table 1 illustrates the percent conversion of monomer to
oligomer at the corrected, theoretical gel point
p.sub.gel(corrected) of alkyd resin formation as a function of the
sum of functional groups on polyol and polyfunctional acid monomers
using Carrothers' theory (Formula II), a k of 0.95, and assuming a
1:1 ratio of polyol monomer to polyfunctional acid monomer. For
example, monomers with a total of five functional groups will reach
the gel point after about 76% conversion, while monomers with a
total of 12 functional groups will reach the gel point after only
about 32% conversion.
TABLE-US-00001 TABLE 1 Effect of the sum of monomer functional
groups on the % monomer conversion at the corrected, theoretical
gel point, p.sub.gel(corrected). Total Number Number of Number of
of Functional % Conversion --OH on --COOH Groups at Polyol Monomer
on Acid Monomer (f.sub.average) the Gel Point 2 2 4 95%* 3 2 5 76%
3 3 6 63% 2 10 12 32% 2 100 102 3.7% *Bifunctional monomers
theoretically form linear polymers. Without being bound by any
particular theory, in practice, some degree of cross-linking occurs
between bifunctional monomers due to side reactions.
[0009] Table 2 illustrates the number of functional groups present
on monomer starting materials that are commonly used to form alkyd
resins.
TABLE-US-00002 TABLE 2 Reactive functionalities of alkyd resin
monomers Monomer Number of Functional Groups Glycerol 3
1,3-Propanediol 2 Adipic acid 2 Maleic anhydride 2 Succinic
anhydride 2 Phthalic anhydride 2 Citric acid 3 Monofunctional fatty
acid 1 Poly(acrylic acid) >>100 Poly(vinyl alcohol)
>>100
[0010] Because the average functionality of a reaction mixture,
f.sub.average, is the weighted sum of the individual reactive
functionalities, the corrected, theoretical gel points of
representative alkyd resin condensation reactions can be estimated
from Formula II, wherein k=0.95, as shown in Table 3.
TABLE-US-00003 TABLE 3 Gel points of alkyd condensation reaction
mixtures estimated by Formula II. Estimated gel point, Reaction
Mixture f.sub.average p.sub.gel(corrected) Glycerol + Phthalic
anhydride (1:1) 2.5 0.76 Glycerol + Adipic acid (1:1) 2.5 0.76
Glycerol + Adipic Acid (5:1) 2.83 0.67 Glycerol + Succinic
Anhydride (1:1) 2.5 0.76 Glycerol + Maleic Anhydride (1:1) 2.5 0.76
Glycerol + Maleic Anhydride (1:2) 2.33 0.82 Glycerol + Maleic
Anhydride (2:1) 2.67 0.71 Glycerol + Citric Acid (1:1) 3 0.63
Glycerol + Citric Acid + Stearic Acid (1:1:1) 2.33 0.82 Glycerol +
Adipic Acid + Stearic Acid (1:1:1) 2 0.95 Glycerol + Poly(acrylic
acid) (1:1) >100 <0.01 Glycerol + Poly(acrylic acid) (50:1)
>10 <0.1
[0011] The degree of monomer conversion in an alkyd resin and the
time required for processing the alkyd resin can be manipulated by
the types of polyfunctional monomers that are used. For example, if
monomers with a low number of functional groups are used, the
resulting alkyd resin will have a high degree of conversion but
will take more time to progress through Stage II, increasing the
manufacture time of the alkyd resin. Because the gel point is
reached more slowly, the alkyd resin material will need prolonged
heating in a mold before becoming cured and obtaining properties
that are characteristic of a thermoset resin. Prolonged heating in
a mold introduces undesirable effects such as the formation of
bubbles and other defects in the final product due to the
liberation of water vapor during condensation. If monomers with a
high number of functional groups are used, the alkyd resin process
will take less time to progress through Stage II, decreasing the
manufacture time. However, the resulting alkyd resin will have a
lower degree of conversion. Because a lower degree of conversion is
achieved at the gel point, the material will need additional
post-curing to become an alkyd material with properties that are
characteristic of a thermoset resin. An ideal system for practical
applications of alkyd resins would include the highest possible
ester conversion to minimize the requirement for additional curing
after gelation, and the shortest amount of processing time.
However, it is currently not possible to produce alkyd resins with
a high degree of conversion in a shortened amount of time.
[0012] The gel point of alkyd resins can also be used as a point of
reference for forming different types of alkyd materials.
Essentially three types of materials exist in the alkyd resin
industry, each formed by one of two different, one-step approaches.
In the first approach, condensation of monomers is allowed to occur
up to but not exceeding the gel point of the material, at which
point the condensation reaction is arrested. The resulting
material, which has undergone about 60% to about 70% conversion is
still prepolymer and is used in the paint industry. The majority of
the cross-linking present in paints is due to the radical
polymerization of residual double bonds instead of a network of
ester linkages.
[0013] In the second approach, the condensation of monomers is
allowed to occur until the prepolymer material has exceeded its gel
point to form a solid, cross-linked network. The resulting material
has properties that are characteristic of thermoset resins.
Coatings and enamels are examples of alkyd materials that are
formed using this second approach. However, enamels are applied to
a surface while in the prepolymer stage and then subjected to
additional heating until the gel point has been exceeded. Therefore
alkyd resin materials in the art have either not reached their gel
points and exist as prepolymer, or have exceeded their gel points
and exist as cross-linked, materials with properties that are
characteristic of thermoset resins.
SUMMARY OF THE INVENTION
[0014] Disclosed herein is a metastable, liquid alkyd resin
precursor that has exceeded its gel point but is not a gel. The
precursor includes a gel point modifier and a prepolymer liquid.
The prepolymer liquid includes oligomeric polyesters, polyols, and
an excipient selected from the group consisting of polyfunctional
acids, anhydrides, and mixtures thereof. The prepolymer liquid has
reached about 50% to about 90% of its corrected, theoretical gel
point, p.sub.gel(corrected). The corrected, theoretical gel point
is determined by Formula II:
p gel ( corrected ) = 2 ( k ) f average , Formula II
##EQU00003##
wherein k is about 0.9 to about 1, and f.sub.average is the sum of
(i) the number of alcohol moieties on the polyol, (ii) the number
of acid moieties on the polyfunctional acid, and (iii) twice the
number of anhydride moieties on the anhydride, divided by the total
number of polyols, polyfunctional acids, and anhydrides.
[0015] Another aspect of the invention is a method of preparing a
metastable, liquid alkyd resin precursor. In this method, a gel
point modifier is added to prepolymer liquid that has reached at
least about 50% of its corrected, theoretical gel point to form the
liquid alkyd resin precursor. The prepolymer liquid includes
oligomeric polyesters, polyols, and an excipient selected from the
group consisting of polyfunctional acids, anhydrides, and mixtures
thereof.
[0016] In yet another aspect, the invention relates to a method of
preparing a fully cross-linked alkyd resin. In this method, a gel
point modifier is added to the prepolymer liquid, generally
described in the preceding paragraph, to form a liquid alkyd resin
precursor. The precursor is then heated while concurrently removing
water that has been generated as a by-product of the condensation
reaction to form the fully cross-linked alkyd resin.
[0017] Additional features of the invention may become apparent to
those skilled in the art from a review of the following detailed
description, taken in conjunction with the drawing, the examples,
and the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] The sole drawing is a schematic representation of the
conversion stages of alkyd resin formation.
DETAILED DESCRIPTION OF THE INVENTION
[0019] It has now been found that the gel point of an alkyd resin
can be manipulated to form a new type of alkyd material. As
previously described, alkyd materials currently exist in one of two
forms: (i) a prepolymer liquid that has not reached its gel point
(e.g. paint), or (ii) a cross-linked, resin that has exceeded its
gel point with properties characteristic of a thermoset resin (e.g.
enamel). Unlike the currently known alkyd materials, the novel
alkyd material of the invention is a metastable, liquid alkyd resin
precursor that has exceeded its gel point but is not a gel. Because
this material has already exceeded its gel point, it will solidify
into a fully cured alkyd resin almost immediately after heating
with the concurrent removal of water.
[0020] It has also been found, quite surprisingly, that it is
possible to manipulate the gel point of an alkyd material through
the use of a gel point modifier to obtain an alkyd resin with a
high degree of monomer conversion in a decreased amount of time.
Often, the onset of gelation in an alkyd material is difficult to
predict or control, which makes the processing of these materials
difficult. The higher the number of functional groups on the
monomers used for alkyd resin formation, the more difficult it is
to control the onset of gelation. Unexpectedly, control over the
onset of gelation can be obtained by adding a gel point modifier to
an alkyd prepolymer liquid, even though the gel point modifier is
itself highly functionalized.
[0021] This novel, metastable, liquid alkyd resin precursor and
novel method of manufacturing alkyd resins are enabled by the timed
addition of a highly functional monomer to the prepolymer liquid
that forms during Stage II of alkyd resin processing. In short,
monomers having a low number of functional groups are subjected to
Stage I and part of Stage II of alkyd resin formation (FIG. 1).
These monomers undergo condensation until they achieve a high
degree of monomer conversion, which is possible due to the low
number of functional groups on the monomers. Once the prepolymer
liquid attains a high degree of monomer conversion but before it
reaches its gel point (between points (b) and (c) of the sole
drawing), the condensation reaction is arrested and a highly
functional monomer is added. This highly functional monomer, termed
a "gel point modifier," effectively shifts the gel point of the
alkyd material to a percent conversion that is lower than the
degree of conversion that has already been achieved (point (a) of
the sole drawing). The result is a liquid, alkyd resin precursor
that has exceeded its gel point, but is not a gel. This liquid,
alkyd resin precursor is metastable and can be stored and shipped
at temperatures of up to about 100.degree. C. This metastable
precursor can subsequently be gelled at will into a fully
cross-linked alkyd resin of any desired shape with good dimensional
stability and mechanical integrity through the addition of heat and
the removal of water.
[0022] For example, a polyol comprising three alcohol moieties can
undergo condensation with an excipient comprising two acid
moieties. The corrected, theoretical gel point of this system
occurs at 76% conversion (Table 1). However, if the condensation
reaction is stopped before the prepolymer liquid reaches its gel
point (e.g. at about 70% conversion) and a gel point modifier
having 10 functional groups is added to the prepolymer liquid, the
corrected, theoretical gel point shifts to, for example, about 10%
conversion, depending on the amount of gel point modifier added.
The prepolymer liquid is already at, for example 70% conversion,
but the corrected, theoretical gel point is now at, for example,
10% conversion. Therefore, a metastable, liquid, alkyd material
results that has exceeded its gel point but is not a gel. Further
condensation of the metastable material does not occur to form a
gel unless the precursor is heated with the concurrent removal of
water.
[0023] Alkyd resins are specifically suited to the novel methods
and materials of this invention because they are unique from other
types of resins (e.g. epoxy resins). Alkyd resins are comprised of
ester cross-links that form from the condensation of a polyol with
an excipient. Because the condensation reaction can be stopped at
any point by, for example cooling the reaction or discontinuing the
removal of water, and then restarted by heating the reaction and
removing water, alkyd resins are able to form a non-gel system that
is ready to be cross-linked at will. The formation of other types
of thermoset resins cannot be stopped and then restarted in the
same way.
[0024] In one aspect, the invention relates to a metastable,
liquid, alkyd resin precursor material that has theoretically
exceeded its gel point but is not a gel. The liquid alkyd resin
precursor includes a gel point modifier and a prepolymer liquid.
The prepolymer liquid includes oligomeric polyesters, polyols, and
an excipient selected from the group consisting of polyfunctional
acids, anhydrides, and mixtures thereof. The monomers of the
prepolymer liquid have preferably undergone about 40% to about 80%%
conversion, more preferably about 70% to about 75% conversion,
resulting in a liquid alkyd resin precursor that has preferably
reached about 50% to about 90%, more preferably about 80% to about
85% of its corrected, theoretical gel point, p.sub.gel(corrected),
as determined by Formula II
p gel ( corrected ) = 2 ( k ) f average Formula II ##EQU00004##
wherein f.sub.average is the sum of (i) the number of alcohol
moieties on the polyol, (ii) the number of acid moieties on the
polyfunctional acid, and (iii) twice the number of anhydride
moieties on the anhydride, divided by the total number of polyols,
polyfunctional acids, and anhydrides; and k is preferably about 0.9
to about 1, more preferably about 0.95. The viscosity of the liquid
alkyd resin precursor is about 0.1 kg m.sup.-1s.sup.-1 to about
10,000 kg m.sup.-1s.sup.-1 at about 160.degree. C. to about
220.degree. C.
[0025] The gel point modifier of the alkyd resin precursor is a
molecule that has at least three, preferably at least four
functional groups selected from the group consisting of acids,
alcohols, amines, thiols, epoxides, anhydrides, and mixtures
thereof. The gel point modifier is preferably present in a
concentration of about 0.1 wt. % to about 10 wt. %, more preferably
about 0.5 wt. % to about 5 wt. %, even more preferably about 1 wt.
%, based on the total weight of the precursor. The gel point
modifier can be an alcohol having primary hydroxyl groups or a
polyfunctional acid, the alcohol or acid having at least four
functional groups. Nonlimiting examples of the polyol or
polyfunctional acid gel point modifier include glycerol,
pentaerythritol, dipentaerythritol, trimethylolpropane,
trimethylolethane, polyglycerol, diglycerol, triglycerol,
hexanetriol, erythritol, xylitol, maltitol, mannitol, polyvinyl
alcohol, succinic acid, trimellitic anhydride, polyacrylic acid,
polymethacrylic acid, and mixtures thereof. In some embodiments,
the gel point modifier is selected from the group consisting of
pentaerythritol, trimethylolpropane, trimethylolethane, polyacrylic
acid, and mixtures thereof.
[0026] The gel point modifier of the alkyd resin precursor can also
be a derivatized fatty acid, fat or oil, such as monoglycerides,
diglycerides, triglycerides, or mixtures thereof. A "derivatized"
fatty acid, fat, or oil is a fatty acid, fat, or oil having pendant
alcohol, epoxide, carboxylic acid, or anhydride groups. "Fatty
acid" refers to a straight chain monocarboxylic acid having a chain
length of 12 to 30 carbon atoms. "Monoglycerides," "diglycerides,"
and "triglycerides" refer to mono-, di- and tri-esters,
respectively, of (i) glycerol and (ii) the same or mixed fatty
acids containing multiple unsaturated double bonds. These fatty
acids, fats, or oils can be derivatized to form highly effective,
multifunctional gel modifiers capable of reacting with either
alcohol or carboxylic acid moieties. The use of derivatized fatty
acids, fats, or oils as gel point modifiers is highly advantageous
because these compounds are able to undergo quick reactions without
producing a water by-product and allow flexibility in formulating
materials with different properties.
[0027] Typical fatty acid, fat, monoglyceride, diglyceride, and
triglyceride oils that are useful herein have been derivatized to
contain pendant carboxylic acid, anhydride, epoxide, or alcohol
groups. Nonlimiting examples of fatty acid gel point modifiers
include derivatized oleic acid, myristoleic acid, palmitoleic acid,
sapienic acid linoleic acid, linolenic acid, arachidonic acid,
eicosapentaenoic acid, and docosahexaenoic acid. In some
embodiments, the fatty acid that is derivatized preferably is
selected from the group consisting of oleic acid, linoleic acid,
linolenic acid, and arachidonic acid. Examples of fat gel point
modifiers include derivatized animal fat. Nonlimiting examples of
monoglyceride oil gel point modifiers include monoglycerides of any
of the derivatized fatty acids described herein. Nonlimiting
examples of diglyceride oil gel point modifiers include
diglycerides of any of the derivatized fatty acids described
herein. Nonlimiting examples of the triglyceride oil gel point
modifier include triglycerides of any of the derivatized fatty
acids described herein. For example, the triglyceride gel point
modifier is selected from the group consisting of derivatized: tall
oil, corn oil, soybean oil, sunflower oil, safflower oil, linseed
oil, perilla oil, cotton seed oil, tung oil, peanut oil, oiticica
oil, hempseed oil, marine oil (e.g. alkali-refined fish oil),
dehydrated castor oil, and mixtures thereof. In some embodiments,
the triglyceride oil that is derivatized preferably is tall oil,
corn oil, soybean oil, sunflower oil, safflower oil, perilla oil,
cotton seed oil, peanut oil, oiticica oil, hempseed oil, marine oil
(e.g. alkali-refined fish oil), and dehydrated castor oil, and more
preferably is soybean oil. The fatty acid, fat, or oil gel point
modifier preferably has been derivatized to include two to four
pendant carboxylic acid, anhydride, epoxide or alcohol groups. A
derivatized fatty acid, fat, or oil gel point modifier with more
than four pendant groups is too reactive, and a fatty acid, fat, or
oil gel point modifier with less than two pendant groups is not
capable of cross-linking.
[0028] The fatty acid, fat, or oil gel point modifier can result
from the derivatization of fatty acid chains containing double
bonds with unsaturated dicarboxylic acids or anhydrides to form
pendant carboxylic acid or anhydride groups. These pendant
carboxylic acid and anhydride groups are able to react with alcohol
moieties. Nonlimiting examples of dicarboxylic acids and anhydrides
that can be used to derivatize fatty acids, fats, or oils include
maleic acid, fumaric acid, citraconic acid, itaconic acid, maleic
anhydride, citraconic anhydride, and itaconic anhydride.
Unsaturated dicarboxylic acids and anhydrides that are too
sterically hindered at or near the point of unsaturation (i.e.
dimethylmaleic anhydride) are not useful herein and may be easily
determined by one skilled in the art. The unsaturated dicarboxylic
acid preferably is maleic acid or maleic anhydride, and is more
preferably maleic anhydride. Maleated triglyceride oils are
commericially available and are inexpensive. For example, maleated
soybean oil is commercially available under the tradename CERAPHYL
NGA (CAS# 68648-66-8) from International Specialty Products Inc.
(ISP; Lombard, Ill.). Maleated fatty acids, fats, and oils can also
be synthesized from a suitable fatty acid, fat, or oil and maleic
acid or maleic anhydride (or another suitable unsaturated
dicarboxylic acid or anhydride as described herein) by thermal
condensation in an "Ene" or "Diels-Alder" adduction.
[0029] The fatty acid, fat, or oil gel point modifier can result
from epoxidation of fatty acid chains containing double bonds to
form pendant alcohol groups. These pendant alcohol groups are able
to react with carboxylic acid moieties. Nonlimiting examples of
epoxidation reagents include peroxy acids (i.e an oxidizing agents
having the chemical formula RCO.sub.3H) such as
m-chloroperoxybenzoic acid (mCPBA), perbenzoic acid, and peracetic
acid, peroxydisulfuric acid, peroxymonosulfuric acid, and hydrogen
peroxide. The epoxidation reagent is preferably a peroxy acid and
is more preferably mCPBA. Epoxidized oils are commericially
available and are inexpensive. For example, epoxidized soybean oil
is commercially available under the tradename VIKOFLEX 7170 (CAS#
8013-07-08) from Arkema (Philadelphia, Pa.). Procedures for
preparing epoxidized fatty acids, fats, or oils are described in
"Advanced Organic Chemistry", 6th Ed. by J. March, McGraw-Hill Book
Company, 2007, p. 1169-1179.
[0030] The prepolymer liquid of the alkyd resin precursor includes
a polyol, an excipient selected from the group consisting of a
polyfunctional acid, an anhydride, and mixtures thereof, and
oligomers formed by the condensation of the polyol with the
excipient. When the excipient is a polyfunctional acid, the molar
ratio of total acid moieties on the polyfunctional acid to alcohol
moieties on the polyol preferably is about 10:1 to about 1:10, more
preferably about 3:1 to about 1:3, and even more preferably about
1:1. When the excipient is an anhydride, the molar ratio of total
anhydride moieties on the anhydride to total alcohol moieties on
the polyol preferably is about 5:1 to about 1:5, preferably about
1.5:1 to about 1:1.5, even more preferably about 0.5:1.
[0031] The polyol of the prepolymer liquid preferably is a molecule
that includes at least two alcohol moieties, preferably at least
three alcohol moieties. Preferably, the alcohol moieties are
primary hydroxyl groups. Nonlimiting examples of polyols include
glycerol, 1,3-propanediol, pentaerythritol, dipentaerythritol,
trimethylolpropane, trimethylolethane, ethylene glycol, diethylene
glycol, polyglycerol, diglycerol, triglycerol, 1,2-propanediol,
1,4-butanediol, neopentylglycol, hexanediol, hexanetriol,
erythritol, xylitol, maltitol, mannitol, polyvinyl alcohol, and
mixtures thereof. In some specific embodiments, the polyol is
selected from the group consisting of glycerol, pentaerythritol,
trimethylolpropane, trimethylolethane, and mixtures thereof.
[0032] The excipient of the prepolymer liquid is selected from the
group consisting of a polyfunctional acid, an anhydride, and
mixtures thereof. The polyfunctional acid preferably is a molecule
that includes at least two carboxylic acid moieties, more
preferably at least three carboxylic acid moieties. The anhydride
preferably is a molecule that includes at least one anhydride
moiety. Nonlimiting examples of the excipient include adipic acid,
maleic acid, succinic acid, sebacic acid, suberic acid, fumaric
acid, glutaric acid, phthalic acid, malonic acid, isophthalic acid,
terephthalic acid, azelaic acid, dimethylolpropionic acid, maleic
anhydride, succinic anhydride, phthalic anhydride, trimellitic
anhydride, polyacrylic acid, polymethacrylic acid, and mixtures
thereof. In some specific embodiments, the excipient is an
anhydride selected from the group consisting of maleic anhydride,
succinic anhydride, phthalic anhydride, and mixtures thereof.
[0033] The metastable, liquid, alkyd resin precursor of the
invention is the first demonstration of an alkyd material that has
surpassed its theoretical gel point, but is not actually a gel.
Advantageously, this material can be stored indefinitely and
shipped at temperatures up to about 100.degree. C. The material can
also be gelled at will with the addition of heat and the concurrent
removal of water, which is liberated as a by-product of the
condensation reaction, to result in a fully cured alkyd resin
product. When the liquid alkyd resin precursor material is
ultimately gelled into an alkyd resin product, the gelation process
can occur almost instantaneously, saving manufacturing and
processing time of the alkyd resin, and significantly reducing the
amount of by-products that form.
[0034] In another aspect, the invention relates to a method for
preparing a liquid alkyd resin precursor. In this method, a gel
point modifier is added to a prepolymer liquid that has reached
about 50% to about 90%, preferably about 80% to about 85% of its
theoretical gel point to form the liquid alkyd resin precursor. In
some embodiments, a small amount of water is added to the liquid
alkyd resin precursor prevent the onset of premature gelation.
[0035] The prepolymer liquid of the alkyd resin precursor includes
a polyol, an excipient selected from the group consisting of a
polyfunctional acid, an anhydride, and mixtures thereof, and
oligomers formed by the condensation of the polyol with the
excipient. When the excipient is a polyfunctional acid, the molar
ratio of total acid moieties on the polyfunctional acid to alcohol
moieties on the polyol preferably is about 10:1 to about 1:10, more
preferably about 3:1 to about 1:3, and even more preferably about
1:1. When the excipient is an anhydride, the molar ratio of total
anhydride moieties on the anhydride to total alcohol moieties on
the polyol preferably is about 5:1 to about 1:5, preferably about
1.5:1 to about 1:1.5, even more preferably about 0.5:1.
[0036] The gel point modifier in this aspect of the invention is a
molecule that includes at least three, preferably at least four
functional groups selected from the group consisting of acids,
alcohols, amines, thiols, and mixtures thereof, as described
herein. The gel point modifier can be an alcohol having primary
hydroxyl groups or a polyfunctional acid, the alcohol or acid
having at least four functional groups. The gel point modifier can
also be a derivatized fatty acid, fat, or oil. Nonlimiting examples
of the gel point modifier are described herein. The gel point
modifier is preferably present in a concentration of about 0.1 wt.
% to about 10 wt. %, more preferably about 0.5 wt. % to about 5 wt.
%, even more preferably about 1 wt. %, based on the total weight of
the precursor.
[0037] The corrected, theoretical gel point in this aspect of the
invention is determined by Formula II, as described above.
[0038] This method allows, for the first time, the formation of a
novel, metastable, alkyd material that has exceeded its gel point,
but is not a gel. As previously described herein, this alkyd resin
precursor can be stored and shipped at temperatures of up to about
100.degree. C. This material can subsequently be gelled at will
into a fully cross-linked alkyd resin with good dimensional
stability and mechanical integrity by heating the liquid alkyd
resin precursor to promote further condensation while removing the
water by-product.
[0039] One way the prepolymer liquid in this aspect of the
invention can be obtained is as described below. A mixture is
prepared that includes a polyol and an excipient selected from the
group consisting of a polyfunctional acid, an anhydride, and
mixtures thereof. This mixture is heated to a temperature
sufficient to promote condensation of the polyol with the
excipient, while concurrently removing water that forms as a
by-product. Condensation is arrested when about 40% to about 80%,
preferably about 70% to about 75%, of the polyol and excipient have
been converted to oligomer, but before the gel point of the
material is reached. The resulting prepolymer liquid includes the
polyol, the excipient, and oligomers formed by the condensation of
the polyol with the excipient, and has reached at about 50% to
about 90%, preferably about 80% to about 85%, of its corrected,
theoretical gel point, as determined by Formula II, described
above.
[0040] In this embodiment of the invention, the condensation
reaction is arrested before the gel point of the material is
reached. The progress of the reaction can be determined by, for
example, monitoring the viscosity of the prepolymer liquid,
calculating the amount of water that should theoretically form as a
by-product of the reaction and then discontinuing the reaction when
the determined amount of water has been collected, and by
monitoring the number of free alcohol and acid moieties that are
present in the reaction solution.
[0041] The condensation reaction can be arrested by any method
typically used to arrest condensation reactions. In one embodiment,
the condensation reaction can be arrested by cooling the prepolymer
liquid to a temperature less than the temperature sufficient to
promote condensation. In another embodiment, the condensation
reaction can be arrested by discontinuing the removal of the water
by-product. Discontinuing the removal of water effectively arrests
the condensation reaction because ester condensation is in
equilibrium with ester hydrolysis as shown below. Ester
condensation is triggered and driven by the removal of water while
ester hydrolysis is triggered and driven by the addition of
water.
##STR00001##
[0042] The mixture of the polyol and the excipient in this
embodiment can be heated to a temperature that promotes
condensation of the polyol with the excipient. In some embodiments,
the mixture can be heated to a temperature of about 100.degree. C.
to about 300.degree. C., preferably about 160.degree. C. to about
220.degree. C.
[0043] The polyol preferably is a molecule that includes at least
two alcohol moieties, more preferably at least three alcohol
moieties, as previously described herein. Preferably, the alcohol
moieties are primary hydroxyl groups. The polyol preferably is
added to the mixture in an amount of about 10 wt. % to about 90 wt.
%, more preferably about 20 wt. % to about 80 wt. %, and still more
preferably about 30 wt. % to about 70 wt. %, based on the total
weight of components in the mixture.
[0044] The excipient is selected from the group consisting of a
polyfunctional acid, an anhydride, and mixtures thereof. The
polyfunctional acid preferably is a molecule that includes at least
two carboxylic acid moieties, more preferably at least three
carboxylic acid moieties, as previously described herein. The
anhydride preferably is a molecule that includes at least one
anhydride moiety, as previously described herein. The excipient
preferably is added to the mixture in an amount of about 10 wt. %
to about 90 wt. %, more preferably about 20 wt. % to about 80 wt.
%, and still more preferably about 30 wt. % to about 70 wt. %,
based on the total weight of components in the mixture.
[0045] When the oligomers of the prepolymer liquid are the result
of the condensation between a polyfunctional acid and polyol, the
molar ratio of total acid moieties on the polyfunctional acid to
alcohol moieties on the polyol is preferably about 10:1 to about
1:10, more preferably about 3:1 to about 1:3, and even more
preferably about 1:1. When the oligomers of the prepolymer liquid
are the result of the condensation between an anhydride and a
polyol, the molar ratio of total anhydride moieties on the
anhydride to total alcohol moieties on the polyol preferably is
about 5:1 to about 1:5, more preferably about 1.5:1 to about 1:1.5,
and even more preferably about 0.5:1.
[0046] In another aspect, the invention relates to a method of
preparing a fully cross-linked alkyd resin. In this method, a gel
point modifier is added to a prepolymer liquid that has reached at
least about 50% to about 90%, preferably about 80% to about 85% of
its corrected, theoretical gel point to form the liquid alkyd resin
precursor. The precursor is then gelled into a fully cross-linked
alkyd resin of any desired shape by heating the precursor to a
temperature sufficient to promote condensation while concurrently
removing the water by-product.
[0047] The prepolymer liquid includes a polyol, an excipient
selected from the group consisting of a polyfunctional acid, an
anhydride, and mixtures thereof, and oligomers that were formed by
the condensation of the polyol with the excipient. When the
excipient is a polyfunctional acid, the molar ratio of total acid
moieties on the polyfunctional acid to alcohol moieties on the
polyol preferably is about 10:1 to about 1:10, more preferably
about 3:1 to about 1:3, and even more preferably about 1:1. When
the excipient is an anhydride, the molar ratio of total anhydride
moieties on the anhydride to total alcohol moieties on the polyol
preferably is about 5:1 to about 1:5, more preferably about 1.5:1
to about 1:1.5, even more preferably about 0.5:1.
[0048] The gel point modifier of this aspect of the invention is a
molecule that comprises at least three, preferably at least four
functional groups selected from the group consisting of acids,
alcohols, amines, thiols, and mixtures thereof, as described
herein. The gel point modifier can be an alcohol having primary
hydroxyl groups or polyfunctional acid, the alcohol or acid
comprising at least four functional groups. The gel point modifier
can also be a derivatized fatty acid, fat or oil. Nonlimiting
examples of the gel point modifier are described herein. The gel
point modifier is preferably present in a concentration as
described herein. The gel point modifier is preferably present in a
concentration of about 0.1 wt. % to about 10 wt. %, more preferably
about 0.5 wt. % to about 5 wt. %, even more preferably about 1 wt.
%, based on the total weight of the precursor.
[0049] According to this aspect of the invention, the alkyd resin
precursor can be heated to a temperature that promotes
condensation. In some embodiments, the precursor can be heated to a
temperature of about 100.degree. C. to about 300.degree. C., more
preferably about 160.degree. C. to about 220.degree. C.
[0050] The method described herein to form fully cross-linked alkyd
resins takes advantage of the strong influence of the number of
individual monomer functional groups on the gel point of the
material by: (i) carrying out the alkyd condensation reaction in
the absence of a highly functional compound to drive the
condensation reaction to a high degree of conversion, (ii)
introducing a small amount of a highly functional molecule that can
effectively shift the gel point to a low value, which is below the
extent of condensation already achieved to form a stable, alkyd
resin precursor, (iii) inducing an almost instantaneous gelation of
the precursor to solidify the reaction mixture into a desired shape
of good dimensional integrity, and (iv) completing the fabrication
of a fully cross-linked alkyd resin article with properties
characteristic of a thermoset resin by further curing the
solidified gel.
[0051] The ability to solidify the alkyd resin precursor into a
prescribed shape before the fabrication of the final product is
advantageous because it reduces the requirement of a long residence
time in a forming operation, such as, for example, molding and
fiber spinning Furthermore, undesirable effects associated with the
curing of a fluid, such as the formation of bubbles and other
defects in the final product due to the liberation of water vapor
during condensation, is significantly reduced by carrying out the
final curing process on a rigid, solid gel instead of on a
fluid.
[0052] This method is also advantageous because it allows control
and predictability over the onset of gelation. As previously
described, two approaches currently exist for the formation of
alkyd materials. In the first approach, condensation of monomers is
allowed to occur up to the gel point of the material, at which
point the condensation reaction is arrested. In the second
approach, the condensation of monomers is allowed to occur until
the prepolymer material has exceeded its gel point to form a solid,
cross-linked network. Often, the onset of gelation is difficult to
predict or control, which makes the processing of these materials
difficult. The higher the number of functional groups on the
monomers, the more difficult it is to control the onset of
gelation.
[0053] It has now been found that control over the onset of
gelation can quite surprisingly be obtained by adding a gel point
modifier to an alkyd prepolymer liquid, even though the gel point
modifier is itself highly functionalized. The addition of a gel
point modifier to a prepolymer solution wherein further
condensation has been arrested, affords a metastable, liquid alkyd
material. This alkyd material is metastable because it has
technically exceeded its gel point but is not a gel. When gelation
is desired, the metastable material is subjected to the addition of
heat and the removal of water to trigger almost immediate gelation.
Therefore, the metastable material allows a significant amount of
control over the onset of gelation of a fully cross-linked alkyd
resin.
EXAMPLES
[0054] The following examples are provided to illustrate the
invention, but are not intended to limit the scope thereof. The
experiment described in Example 1 demonstrates the formation of a
glycerol-maleate cross-linked alkyd resin, not according to the
invention, without the use of a gel point modifier. The experiment
described in Example 2 demonstrates the formation of a
glycerol-maleate cross-linked alkyd resin, according to the
invention, with the use of a gel point modifier.
Example 1
[0055] In this example, a glycerol-maleate cross-linked resin is
prepared without a gel point modifier. Glycerol (101.30 g, 1.1 mol;
Superol, P&G Chemicals), methanesulfonic acid (0.52 g, 0.25 wt
%, Aldrich) and a stir bar were added to a beaker. The mixture was
warmed to about 60.degree. C. while stirring moderately. Maleic
anhydride (107.87 g, 1.1 mol; Acros) was slowly added to the
warming/stirring glycerol solution until all of the material had
been added. Addition of the maleic anhydride continued as it melted
and dispersed. The temperature was slowly raised to 150.degree. C.
while the viscosity and temperature of the solution was monitored
with a viscometer (Brookfield) and thermometer. Heating and
stirring continued at 150.degree. C. until the material viscosity
was high enough to prevent the stir bar from spinning. The total
reaction time was about 47 min.
Example 2
[0056] In this example, a glycerol-maleate cross-linked resin is
prepared with a gel point modifier. Glycerol (101.30 g, 1.1 mol;
Superol, P&G Chemicals), methanesulfonic acid (0.52 g, 0.25 wt
%, Aldrich) and a stir bar were added to a beaker. The mixture was
warmed to about 60.degree. C. while stirring moderately. Maleic
anhydride (107.87 g, 1.1 mol; Acros) was slowly added to the
warming/stirring glycerol solution until all the material had been
added. The temperature was slowly raised to 150.degree. C. while
the viscosity and temperature of the solution was monitored with a
viscometer (Brookfield) and thermometer. After 15 min at
150.degree. C., pentaerythritol (10.46 g, 5 wt %, Aldrich) was
added to the solution while maintaining a constant temperature and
stir rate. Heating and stirring continued at 150.degree. C. until
the material viscosity was high enough to prevent the stir bar from
spinning. The total reaction time was about 38 min.
[0057] The dimensions and values disclosed herein are not to be
understood as being strictly limited to the exact numerical values
recited. Instead, unless otherwise specified, each such dimension
is intended to mean both the recited value and a functionally
equivalent range surrounding that value. For example, a dimension
disclosed as "40 mm" is intended to mean "about 40 mm"
[0058] Every document cited herein, including any cross referenced
or related patent or application, is hereby incorporated herein by
reference in its entirety unless expressly excluded or otherwise
limited. The citation of any document is not an admission that it
is prior art with respect to any invention disclosed or claimed
herein or that it alone, or in any combination with any other
reference or references, teaches, suggests or discloses any such
invention. Further, to the extent that any meaning or definition of
a term in this document conflicts with any meaning or definition of
the same term in a document incorporated by reference, the meaning
or definition assigned to that term in this document shall
govern.
[0059] While particular embodiments of the present invention have
been illustrated and described, it would be obvious to those
skilled in the art that various other changes and modifications can
be made without departing from the spirit and scope of the
invention. It is therefore intended to cover in the appended claims
all such changes and modifications that are within the scope of
this invention.
* * * * *